In certain types of power systems, for example, for helicopters, two turbine engines are connected to drive a single load, with each engine being capable of supplying the power requirements to continue the flight plan, even if the other engine is shut down. The power output from the two engines is applied to the rotor through a gear box which includes special clutches, which may be of a type known as Sprag clutches, to decouple either of the engines which is running at a lower speed than the others, from the drive train. In such systems it is desired that a number of factors be taken into consideration in controlling the engines, including (1) avoiding applying more power to the output gear train than it is capable of handling, (2) providing over-temperature control for the engines, (3) controlling the engine speed in accordance with pilot input, and (4) operating the two engines to deliver substantially equal torque to the output gear train. In such a system, if the individual controls and/or feedback loops for the various functions are individually implemented, it is possible, under adverse conditions, that the various engine controls will operate against one another and will cause some cycling of the engine or other controls. In addition, the response of the system may be made somewhat more "loose" than might be desired, in order to avoid adverse interaction between the various control functions and the resulting undesired cycling mentioned above.
Accordingly, an important object of the present invention is to provide an integrated dual engine control system with a single output control signal for each engine, thereby permitting more accurate and tighter system control and response.